Heat treated glass panes which are toughened to impart safety properties and/or are bent are required for a large number of areas of application, for example for architectural or motor vehicle glazings. It is known that for thermally toughening and/or bending glass panes it is necessary to process the glass panes by a heat treatment at temperatures near or above the softening point of the glass used and then either to toughen them by rapid cooling or to bend them with the aid of bending means. The relevant temperature range for standard float glass of the soda lime silica type is typically about 580-690° C., the glass panes being kept in this temperature range for several minutes before initiating the actual toughening and/or bending process.
“Heat treatment”, “heat treated” and “heat treatable” in the following description and in the claims refer to thermal bending and/or toughening processes such as mentioned before and to other thermal processes during which a coated glass pane reaches temperatures in the range of about 580-690° C. for a period of several minutes, e.g., for up to about 10 minutes. A coated glass pane is deemed to be heat treatable if it survives a heat treatment without significant damage, typical damages caused by heat treatments being high haze values, pin holes or spots.
Difficulties can arise if glass panes are to be provided with coatings, particularly with coatings comprising at least one silver-based functional layer, e.g., to impart low-e and/or solar control properties to reduce the energy transfer through the coated glass pane in certain spectral regions. Such coatings are not of themselves heat treatable. Silver-based functional layers are usually embedded between lower and upper anti-reflection layers and, optionally, further auxiliary layers which protect them, modify the reflection and transmission characteristics of the coating, etc.
It would be desirable if coatings able to withstand heat treatments without significant damage (=heat treatable coatings) could be made available. It would be particularly desirable if heat treatable coatings able to withstand heat treatments without a significant change of their optical properties, e.g. light transmittance and reflection colour, as reflected in low ΔE* values, could be made available.
EP 0 718 250 B1 discloses heat treatable coated glass panes with a low-e and/or solar control coating comprising a lower anti-reflection layer, a silver-based functional layer, a barrier layer and an outer anti-reflection layer, wherein the lower and upper anti-reflection layers each comprise partial layers having diffusion barrier properties and wherein the top partial layer of the lower anti-reflection layer comprises an oxide of Zn. While AlN is mentioned as a material for both partial layers having diffusion barrier properties, silicon compounds such as silicon nitride (Si3N4) or silicon oxinitride (SiOxNy) are disclosed as most preferred materials for these partial layers. The upper anti-reflection layer may comprise further partial layers of an oxide of Zn arranged below a silicon nitride layer. The metallic barrier layer protects the silver-based functional layer during the deposition of the preceding layers of the coating and during a subsequent heat treatment by capturing oxygen and thereby being partially or fully oxidized. According to the examples of the prior publication coated glass panes with coatings, the anti-reflection layers of which comprise partial layers of Si3N4 or SiO2 as diffusion barriers, show only small changes of their light transmittance (ΔTL at most 2%) and their reflection colour when heat treated at temperatures between 620 and 640° C. Known coated glass panes provide however of a less than optimum sheet resistance at a given thickness of the silver-based functional layer. Their production, specifically when using metallic barrier layers, is difficult to control and certain of the known coated glass panes show an unacceptably high damage level or an unacceptably low mechanical robustness after a heat treatment.
EP 1 154 963 B1 discloses heat treatable coated glass panes with a low-e and/or solar control coating comprising a lower anti-reflection layer, a silver-based functional layer, a barrier layer and an outer anti-reflection layer, wherein the lower and/or upper anti-reflection layers comprise partial layers of (oxi)nitrides of aluminium and of metal oxides, preferably of mixed oxides of Zn and Al. Barrier layers are provided on the silver-based functional layers which may be either metallic or suboxidic. The coatings are designed such that the light transmittance of a coated glass pane changes by at least 2.5% and preferably significantly more during a heat treatment. EP 1 154 963 B1 does not disclose heat treatable coated glass panes having stable optical properties, specifically a stable light transmittance, during a heat treatment. Coated glass panes according to EP 1 154 963 B1 display haze values of no less than 0.2% after a heat treatment.
EP 1 140 721 B1 discloses a method of sputtering barrier layers of metal-doped metal oxides such as Al-doped ZnO from metal-doped metal oxide targets, which barrier layers are to be arranged on top of the silver-based functional layer of certain low-e and/or solar control coatings. The lower anti-reflection layer of these coatings may comprise a base layer of an oxide of Zn and Sn and a top layer of ZnO, and the upper anti-reflection layer may comprise a layer of an oxide of Zn and Sn. At least some of the coated glass panes disclosed in EP 1 140 721 B1 are believed to be heat treatable and to show only small changes of their optical properties during a heat treatment. However it has been found that coatings of the type disclosed in this prior publication tend to be highly susceptible to visible haze formation during a heat treatment.
EP 1 644 296 A2 discloses heat treatable low-e and/or solar control coatings comprising an upper anti-reflection layer of a nitride such as Si3N4 covered by a final oxide layer and specifically discloses a coating of the layer sequence: glass/Si3N4/ZnO/Ag/opt. metal barrier/ZnO/Si3N4/metal oxide cover layer.
Heat treatable low-e and/or solar control coatings with a lower anti-reflection layer comprising an Al (oxi)nitride base layer and top layer of Al-doped ZnO and with an upper anti-reflection layer comprising an Al-doped ZnO layer and an outermost Al nitride layer are proposed by EP 1 147 066 B1. Further publications to be mentioned are EP 1 720 699 A2 and EP 1 529 761 A1.